Method of production of refractory metal leaf



MOLYBDENUM & cam/v6 v T4NT4LUM /MOL YBDENUM POL/SHED ROLL Filed Oct.'14, 1932 M m m B. c. GARDNER ET AL METHOD OF PRODUCTION OF REFRACTORYMETAL LEAF m/vmu/M .OOl/A/CH.

MOVLYBDENUM .005 INCI-l.

MOLVBDENUMOOS/M & COAT/N6.

.00025/NCH.

M M w m .005 INCH.

Nov. 6, 1934.

iNVENTORS,

v m/v ALUM .OOOOl/ucn.

055mm c. GARDNER &

RUSSELL H. VAR/AN.

' ATTORNEY Patented Nov. 6, 1934 5 UNITED STATES PAT ENT OFFICE1,979,539 METHOD OF PRODUCTION OF REFRACTORY METAL LEAF Bernard 0.Gardner and Russell H.

' Philadelphia, Pa.,

Varian,

assignors to Television Laboratories, Ltd., San Francisco, Calif., acorporation of California Application October 14, 1932, Serial No.637,772

" 1 Claims. (01. eta-1a) a refractory metal leaf having a high polishimparted by a rolling process; to produce a tantalum leaf having athickness less than .00001 inch; to provide means of handling such thinmetal leaf; to provide methods whereby refractory metal may be rolled toextreme thiimess; to provide a material for use as a lubricant in arolling process which produces thin refractory metal leaf; and toprovide a method of annealing thin sheets of refractory metal. 1

Other objects of our invention will be apparent or will be specificallypointed out in the description forming a part of this specification, butwe do not limit ourselves to the embodiment of the invention'hereindescribed, as various forms may be adopted within the scope of theclaims.

Referring to the drawing, which diagrammatically illustrates varioussteps of our invention:

Figure 1 shows the formation of a book, or container for refractorymetal. Figure 2 shows the book of Figure 1 passing through polishedrolls.

Figure-3 shows'the formation of another type of book.

Figured shows the book of Figure 3 passing through the rolls.

Figure 5 shows analternative form of book for extremely fine leaf.

Figure 6' shows the book of Figure 5 passing through the rolls.

Figure 7 shows a method of mounting the fine mat Figure 8 shows a methodof floating extremely fine leaf on water.

While refractory metals, such as tungsten,

-molybdenum and tantalum may be drawn into fine wire, they have not, asfar as we are aware,

been fashioned into leaf form. Ordinary rolling processes willproducesheet with a minimum of perhaps .0005 inch although a sheet .001 inch isthe minimum supplied by most commercial producers. y

In its broadest sense our-invention comprises a method of rollingrefractory metal such as tantalum forexample to a substantially uniformthickness of less than .000005 inch. The methodjcomprises repeatedrollings of a book -formed of sheet metal, the book containing the metalto be reduced to leaf form. We also have invented a lubricant to beplaced between the leaf and the book so that the leaf may not stick tothe book covers, or we may remove the book material with an acid whichdoes not attack the leaf. These methods produce a leaf having adesirable. high polish.

While we employ certain differing procedures in order to obtaindifferent thicknesses of leaf we prefer to start, in a method wherein itis desired to produce tantalum leaf, witha book formed from molybdenumsheet..005 inch thick, by folding in the center to form two covers, asshown in Figure 1.

A square of .001 inch tantalum sheet preferably about 1x inch. is firstthoroughly degassed and annealed in vacuo as nearly as possible to its'melting point or, in practice to about 2400 C. This is preferably doneby enclosing the tantalum in a tungsten cylinder of small diameter, andheating the cylinder to incandescence by using it as a filament in anevacuated container, while the vacuum pumps are operating.

The tantalum is then removed and placed in the book, which is cut to 1inch across the fold by about 2 inches length of each cover. The insideof the molybdenum covers are polished to an extreme fineness and thetantalum placed so that its 1 inch width corresponds with the foldwidthof 1 inch, leaving 1 inches toward the open end of the coversfor-expansion of the tantalum. The tantalum is placed with one edgedirectly against thefold.

Closing the book, it is then fed through polished jewelers rollsrepeatedly, always starting the book through-fold first, as shown inFigure 2.

The 'book is rolled until the tantalum has nearly doubled its area, i.e.", to about 1x1 inch.

There is practically no expansion laterally of the rolls, thetantalumenlarging toward the open end of the book.

, After few rollings, the polished surface of the molybdenum isexamined, and if it appears 'has deteriorated, leaf cannot be produced.

The repeated rollings are then continued until a thickness of about.0002 inch is obtained,

when it is desirable to re-anneal, and cut to size again. New polishedbooks are preferably provided at thicknesses of approximately .0000?inch, and .00004 inch, until a thickness of .000025 inch is reached,which is as far as we we roll nickel sheet to .0002 inch in exactly thesame manner as abovedescribed for tantalum. We then form a book of thenickel, place a piece of the .000025 inch tantalum therein as describedfor the start of the original process, and then place the nickel bookinside of a polished molybdenum book, with the fold of one against thefold of the other, as shown in Figure 3. The nickel, having been rolledbetween polished molybdenum, will have a high polish also.

, performed under water.

The nickel is then dissolved away in HNO; as

The combined books are inserted in the rolls as shown in Figure 4 andthe repeated rollings started. The nickel book increases in area, anddecreases in thickness, as does the tantalum inside. The molybdenumcovers are replaced frequently, but the nickel book is notdisturbedfuntil the increase in area indicates that the tantalum hasdecreased to .00001 inch. 1

The nickel-tantalum book now cannot be opened, as the rolling has causedthemto stick together, so the entire book is spot welded to a frame,usually a frame in which the leaf is intended to be used. This weldingis preferably shown in Figure 7, and as the frame is made of a materialnot soluble in the acid, the tantalum remains. It is washed and dried,.and is then ready for use as a leafhaving a high polish and a uniformthickness of .0000Linch. I

We have found, in the welding process, tha the weld spots are notattacked by the acid, even though nickel is between the tantalum and theframe.- It is our belief the nickel has melted away directly at thespot, allowing the tantalum to come in direct contact with the frame. Atleast, the acid does not loosen the welds.

We have found it desirable to discontinue the nickel-tantalum book aftera thickness of .00001 inch is reached, and if a still thinner leaf Yethe tantalum from sticking to the-metal of the covers. Other futmes, e.g., those of aluminumor even soot,'which will deposit an exceedinglyfine coating are satisfactory, as we believe the lubricant to be pureLvPhysical in character.

opened, the leaf will be free, and will float out 'on' We then place acut and annealed piece of .00025 inch tantalum leaf, produced by; one ofthe above described methods, in the fold of the coated molybdenum bookinch. k i

The molybdenum book. may then be carefully and roll to .000005 a watersurface asshowngin Figure 8. The

finished leaf may then be welded to a frame, or utilized in any mannerdesired.

The methods as above described have been utilized to produce arefractory metal leaf of extreme thinness, and when such leaf isproduced by those methods, a high polish is carried all the way throughto the final product. Even the thinnest leaf produced, that having athickness of less than .000005 inch is remarkably uniform in thickness,being free bothfrom thin spots, and from wedging or other grossdimensional changes.

While the method has been described as applied to the sizes andmaterials which we have found most suitable to our own work, theusefulness of the method is not thus hmited. We have substitutedstainless steel for nickel and even for the molybdenum with a fairdegree of success, although theprocess cannot be carried as far, in asingle stage, when this is done. Nickel can be rolled very thin betweenmolybdenum or tantalum leaves, for example.

the process of drawing out nickel between stainless steel, or stainlesssteel between molybdenum. The use of a less desirable casing materialmay no in some degree be compensated for by imparting to it a higherpolish,'and by more frequent casing changes, as the breakdown of thefoil is always preceded by the deterioration of the inner surface of thebook; as soon as this surface-begins 5 to have an etched appearance thecasing should be changed.

As far as is known the above described method is the only way by whichrefractory metals may be formed into leaf of extreme thinness, but itshould be understood that the processes described will produce leafequally well from metals which have hitherto been reduced to leaf form,by other methods well known in the art. All metal leafs, however,produced by the processes as described, will be characterized by theirhigh polish.

We claim:

1. The method of producing a metal leaf which comprises enclosing saidmetal in a polished sheet metal container, repeatedly rolling saidcontainer until said polish is impaired, inserting said metal in a newlypolished container, and repeating said rolling.

. 2. The method of producing a metal leaf which comprises enclosing saidmetal in a polished con- 5 tainer, repeatedly rolling said container,removing the partly rolled leaf, enclosing said partly rolled leaf in a'ne'wlypolished sheet metal container, coating the interior wa1ls of saidlast mentioned container with a deposit from the fumes of metal burnedin air, and repeatedly rolling'thebook thus formed.

. 3. The method of producing a metal leaf which comprises enclosing saidmetal in a polished container, repeatedly rolling said container, remov-5 ing the partly rolled leaf, enclosing said partly rolled leaf in anewly polished sheet metal container, coating the interiorwalls of saidlast mentioned container with a deposit from the fumes of metal burnedin air, rolling the 5o book thus formed, opening said book, and allowingthe finished leaf to float free of said book on the surface of a liquid.I

4=. The method of producing a refractory metal leaf which comprisesenclosing said refractory metal in a polished refractory container,repeatedly rolling said container, removing the partly rolled leaf,enclosing said partly rolled leaf in a polished non-refractory metalcontainer; enclosing said non-refractory container in a polishedrefractory container, repeatedly rolling the'book thus formed, removingsaid non-refractory, container, and dissolving said non-refractory metalin a liquid which will not attack the resultant refractory metal leaf.

5. The method of producing a refractory metal leaf whichcomprisesenclosing said refractory metal in a polished refractorycontainer, repeatedly rolling said container, removing the partly rolledleaf. enclosing said partly rolled leaf in a polish ed non-refractorymetal container, enclos ing said non-refractory container in a polishedrefractory container, repeatedly rolling the book thus formed, removingsaid non-refractory container, and dissolving said non-refractory metalin acid which will not attack said leaf. I

6. In the method of producing a delicate metal leaf by rolling betweenmetal covers joined at one edge, the step of opening said covers in aliquid BERNARD c. GARDNER. RUSSELL 1-1.1 VARIAN I M ss

